SPARC, programming A technique used on the
SPARC to reduce
after a branch instruction (the "delay instruction" in the
"delay slot"). If there is no useful instruction which can be
placed in the delay slot then the "annul bit" on the control
transfer instruction can be set, preventing execution of the
delay instruction (unless the control transfer is conditional
and is taken).
Annulled branches are indicated in SPARC assembler language by
LOOP: ...
CMP %L0,10
BLE,A LOOP
ADD %L2, %L3, #L4
If the delay instruction is also a control transfer
instruction then it gets more complicated. Both control
transfer instructions are executed (but not the following
instruction) and, assuming they are both taken, control is
transferred briefly to the destination of the first and then
immediately to the destination of the second.
(2001-06-26)